A big chunk of Facebook’s recent success comes from its “fan pages,” which big brands use to connect with customers–and spend big dollars to promote.

So are they getting their money’s worth? Maybe–if they’re not spending much more than a double latte per fan.

Each fan is worth an average of $3.60 a year, based on the number of media impressions he or she generates via Facebook users’ “newsfeeds,” according to social media consultancy Vitrue.

AllFacebook explains the math:

If a brand posts to their Facebook Fan Page twice a day and have a million fans, that’s 60M impressions per month in the collective “news feed”. Vitrue used a figure of $5 CPM (Cost per thousand impressions), so 60M impressions would result in $300K/month of media value. I.e., what the brand might have to spend elsewhere to get the same eyeballs. That $300K /month is $3.6M/ year, meaning that with 1M fans, the average value is $3.6 per fan.

Interestingly, Vitrue’s numbers don’t try to account for the secondary impressions fan pages generate, when fans’ friends see their activity. But I’m sure that Facebook, and the vendors who help the social network promote its fan pages, will point that out.